Equity Incentive Program - Additional Information (Details) - USD ($)
$ in Millions |
3 Months Ended |
Mar. 31, 2018 |
Mar. 31, 2017 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Allocated share-based compensation expense |
$ 7.0
|
$ 5.9
|
| SSARs |
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Unrecognized compensation expense |
0.0
|
|
| Stock Options |
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Unrecognized compensation expense |
$ 10.1
|
|
| Weighted average period for compensation expense to be recognized |
1 year 6 months
|
|
| Restricted Stock Units (RSUs) |
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Unrecognized compensation expense |
$ 37.3
|
|
| Weighted average period for compensation expense to be recognized |
1 year 7 months
|
|
| Performance Shares |
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Unrecognized compensation expense |
$ 6.6
|
|
| Weighted average period for compensation expense to be recognized |
2 years 7 months
|
|
| Minimum | Performance Shares |
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Percentage increase of initial grant value |
0.00%
|
|
| Maximum | Performance Shares |
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
| Percentage increase of initial grant value |
225.00%
|
|